Between April 21 and July 14, the HEPI Fluid system Accumulators were properly charged--19632.  The check of the charging obviously has risks though, not only does the Pump need to be spun down taking down the entire SEI isolation, the checking of the pressure via the schrader valve of the accumulator may cause it to start leaking.  This is what I expect happened at EndY on 14 July.  When I was at EndY Tuesday 21 July looking at the reference voltage of the pressure sensors (attempting to learn why the sensors are noisy,) I noted the HEPI reservoir Fluid level was dramatically down.  Yesterday I found the schrader valve was indeed leaking and needed replacement.

Fortunately, it appears the platform is not that sensitive to the loss of just a single accumulator, or it maybe more importantly depend on where that accumulator is in the system.  Attached are coherence plots between the servo pressure and the HEPI and ISI inertial sensors.  The reference traces (thick pale) are from 11 July, before my confirming measurement on July 14.  The current traces (thin dark) are from the early morning hours yesterday after I saw the low fluid level.  While there are a scattering of a few peaks of increased coherence in no instance are they in adjacent frequency bins.  There a few higher frequency (between 0.5 and 3hz) spikes that approach 0.9, too large for comfort of course but there are no broadband areas of increased coherence.  Is this meaningful?  Still, the fluid levels must be watched and accumulators checked at the first sign of lower fluid level in the reservoir.

I'll look at this again in a couple days and see if these spikes go away since the charging of this one accumulator.  Also, I need to check the affect of a lost accumulator on the fluid level in the corner station.  The actual fluid 'loss' should be the same but the reservoir is larger so the drop should be less.  Still, the loss of one accumulator would be noticeable.